Posted by jlwile on September 12, 2011
Antibiotic resistance in bacteria is often cited as evidence for evolution. For example, in his book, The Greatest Show on Earth: The Evidence for Evolution, Richard Dawkins says:1
Many bacterial strains have evolved resistance to antibiotics in spectacularly short periods. After all, the first antibiotic, penicillin, was developed, heroically, by Florey and Chain as recently as the Second World War. New antibiotics have been coming out at frequent intervals since then, and bacteria have evolved resistance to just about every one of them.
However, we’ve known for quite some time that at least some antibiotic resistance did not evolve after the production of antibiotics. Instead, it existed before antibiotics were developed. For example, in 1988, bacteria were recovered from the frozen bodies of Arctic Explorers who died in 1845, long before antibiotics had been produced. When the bacteria were revived, some were found to be already resistant to certain antibiotics.2 So contrary to Dawkins’s claim, it is not at all clear that bacteria have evolved resistance to just about every antibiotic. Some possessed resistance before antibiotics were ever made
A recent study published in the journal Nature confirms this fact at a very basic level.
Researchers from McMaster University studied bacterial DNA that was extracted from soil frozen in the permafrost of the Yukon Territories. These genes were found in the same soil in which mammoth genes were found, and since we know that mammoths died out long before the development of antibiotics, we know these bacterial genes existed long before the development of antibiotics. What did the researchers find among these genes? They found the genes that provide modern bacteria with resistance to several different kinds of antibiotics.3
Then the researchers went a step further. They took one of the genes (in modern bacteria, this gene provides resistance to the antibiotic known as vancomycin) and produced the protein precisely the way the gene would have instructed the bacterium to produce it all those many years ago. This, in and of itself, is an amazing feat since they essentially made a protein that a bacterium living at the time of the mammoths would have made! They then tested that protein and showed that it does exactly the same thing that it does in modern, vancomycin-resistant bacteria.
This, then, is conclusive evidence that bacteria already had the genetic information necessary to be resistant to some antibiotics. As the authors themselves note:
These results show conclusively that antibiotic resistance is a natural phenomenon that predates the modern selective pressure of clinical antibiotic use.
In other words, bacteria did not evolve resistance to antibiotics in response to their production. Instead, they already had the ability to resist antibiotics before their production.
Does this mean that all antibiotic resistance is built into bacteria? No, it does not. Some bacterial resistance does occur as a result of mutation. For example, a bacterium can become resistant to streptomycin if a mutation causes a defect in the bacterium’s protein-making factory, which is called the ribosome. That defect keeps streptomycin from binding to the ribosome, which makes streptomycin ineffective against the bacterium. However, such a mutation results in a loss of genetic information, because the defect causes the ribosome to be much less efficient at its job.4 So while the mutation does provide resistance to streptomycin, it does so by simply degrading something that already exists, rather than building up something new in the bacterium.
So contrary to what Richard Dawkins and many others state, bacterial resistance offers no evidence for evolution. In some cases, antibiotic resistance is conferred by genes that existed in bacteria long before the antibiotics were made. In other cases, antibiotic resistance is conferred by mutations that degrade structures which existed in bacteria long before the antibiotics were made. Either way, nothing new is being produced.
1. Richard Dawkins, et al., The Greatest Show on Earth: The Evidence for Evolution, 2009, p. 132
Return to Text
2. R. McQuire, “Eerie: human Arctic fossils yield resistant bacteria,” Medical Tribune, December 29, 1988, pp. 1, 23
Return to Text
3. Vanessa M. D’Costa, et. al., “Antibiotic Resistance is Ancient,” Nature, doi:10.1038/nature10388, 2011
Return to Text
4. Gartner, T. and Orias, E., “Effects of mutations to streptomycin resistance on the rate of translation of mutant genetic information,” Journal of Bacteriology 91:1021–1028, 1966.
Return to Text